Reduction of metallic oxides by late Ar–H2–N2 postdischarges. II. Applications to iron oxides

Abstract

In this second part of a study dealing with the reduction of metallic oxide, iron oxide (Fe2O3) is treated by Ar–N2–H2 post discharges. The influence of the composition of both the gas mixture and the temperature on the reduction kinetics was measured between 783 and 868 K. If CuO is reduced to Cu (see Part I of the study), Fe2O3 is reduced to Fe2N1−x or Fe depending on the gas mixture composition. Measurements of the activation energies of the reduction reactions suggest that the reduction mechanisms of Fe2O3 are limited by the diffusion of oxygen in ε- Fe2N1−x. Similar conclusions to those drawn in the case of copper suggest that atomic nitrogen can reduce these oxides, but the reduction kinetics by this specie is much slower than by H. It is also confirmed that atomic hydrogen seems to affect the internal reaction at the interfaces of the sublayer oxides and modifies the activation energy of the growth processes. Finally, the reduction of titanium oxide (TiO2) at 873 K is not observed, and the reduction kinetics, and thus the treatment temperature, seems to depend on the metal–oxygen binding energy.